This invention relates to an ink jet printhead. More particularly, the invention relates to an ink jet printhead that includes nozzle-clearing mechanisms.
Ink jet printheads of the type manufactured using micro-electromechanical systems technology have been proposed in a construction using nozzle chambers formed in layers on the top of a substrate with nozzle chambers formed in the layers. Each chamber is provided with a movable paddle actuated by some form of actuator to force ink in a drop through the nozzle associated with the chamber upon receipt of an electrical signal to the actuator. Such a construction is typified by the disclosure in International Patent Application PCT/AU99/00894 to the Applicant.
The present invention stems from the realisation that there are advantages to be gained by dispensing with the paddles and causing ink drops to be forced from the nozzle by decreasing the size of the nozzle chamber. It has been realised that this can be achieved by causing the actuator to move the nozzle itself downwardly in the chamber thus dispensing with the paddle, simplifying construction and providing an environment which is less prone to the leakage of ink from the nozzle chamber.
Furthermore, Applicant has identified that it would be useful to incorporate a mechanism whereby ink ejection ports could be kept clear of obstructions, such as dried ink or paper dust.
According to the invention there is provided an ink jet printhead that comprises
a substrate; and
a plurality of micro-electromechanical nozzle arrangements positioned on the substrate, each nozzle arrangement comprising
a nozzle chamber defining structure having a fixed portion that is fast with the substrate and a movable portion that is displaceable with respect to the substrate and that defines an ink ejection port, the movable portion and fixed portion together defining a nozzle chamber and the movable portion being displaceable towards and away from the substrate to reduce and subsequently increase a volume of the nozzle chamber so that ink is ejected from the ink ejection port; and
an actuator that is operatively engaged with the movable portion to displace the movable portion with respect to the fixed portion, wherein a projection is positioned on the substrate, the projection being configured so that, when the movable portion is displaced towards the substrate, the projection extends through the ink ejection port.
The substrate may define a plurality of ink conduits, each ink conduit being in fluid communication with a respective nozzle chamber.
The movable portion may include a roof portion and a sidewall depending from a periphery of the roof wall. The fixed portion may include a complementary sidewall, the sidewalls being configured to overlap when the movable portion is displaced towards the substrate.
Each projection may be in the form of a rod-like structure. Each rod-like structure may be mounted on a respective bridge member that spans each ink conduit.